Article pubs.acs.org/EF
Interaction Characteristics of Mineral Matter and Nitrogen during Sewage Sludge Pyrolysis Li-Hong Wei,* Li-Na Wen, Mei-Jia Liu, and Tian-Hua Yang College of Energy and Environment, Shenyang Aerospace University, Shenyang, Liaoning 110136, People’s Republic of China ABSTRACT: The conversion of nitrogen-containing species in sludge is influenced by mineral matter. Raw sludge and demineralized sludge were pyrolyzed in a fixed-bed reactor in the temperature range of 500−800 °C to investigate the roles of the temperature and mineral matter on the nitrogen conversion in sewage sludge. To gain an in-depth knowledge and understanding of the nitrogen transformation mechanisms, we characterized the nitrogen-containing functional groups in raw sludge and chars via X-ray photoelectron spectroscopy, and the NOx precursors (HCN and NH3) were identified using a spectrophotometric method. According to the results, mineral matter has been proven to be able to affect the yields of char N, gas N, and other N (nitrogen in tar, N2, NO, and others). The interaction between mineral matter and N-containing species in sewage sludge is strongly limited by the temperature. Mineral matter inhibits char N conversion at 500−600 °C and promotes char N conversion within the range of 600−800 °C. Meanwhile, mineral matter suppresses the yield of HCN but promotes the production of NH3.
1. INTRODUCTION Municipal sewage sludge (SS) constitutes the largest volume of waste in municipal wastewater treatment plants in China for the past several years. The production of SS anticipates close to 400 million tons [20% demineralized sludge (DS)] in 2015 and is expected to increase up to 500 million tons in 2020 in China. Pyrolysis is an important process of SS during combustion and gasification, converting sludge from waste to useful products. Recently, increasing attention has been focused on the thermal processes of SS for energy recovery through pyrolysis technology. However, the nitrogen content in sludge reaches up to 2.4−9 wt %,1−3 which is considerably higher than that in coal (
